roles.js

// example input
const input = `
Disc 1
Composed by
  John Doe (1, 2, 6~10)
  Foo Bar (3)

Arranged by
  Some Guy (1~10)

Disc 2
Composed by
  John Doe (3, 5, 7)

Arranged by
  Foo Bar (1)
  Baz Qux (2~6)
`

const parsed = {}
let curDisc
let curRole
for (const rawline of input.split('\n')) {
  const line = rawline.trim()
  if (!line) {
    continue
  }
  const newDisc = line.match(/Disc (\d+)$/i)
  if (newDisc) {
    curDisc = Number(newDisc[1])
    curRole = undefined
    continue
  }
  const newRole = line.match(/^(.*)(?: by|:| by:)$/i)
  if (newRole) {
    curRole = newRole[1]
    continue
  }
  const artistsAndTracks = line.match(/^(.*) \(([\d,-~ ]+)\)$/)
  if (artistsAndTracks) {
    const [, rawartists, rawtracks] = artistsAndTracks
    const artists = rawartists.split(',').map(a => a.trim())
    const tracks = rawtracks.split(',').map(t => {
      const range = t.trim().match(/^(\d+)[-~](\d+)$/)
      if (range) {
        const [, rawfirst, rawlast] = range
        const first = Number(rawfirst)
        const last = Number(rawlast)
        if (!(last > first)) {
          throw new RangeError('range not start~end')
        }
        const nums = []
        for (let i = first; i <= last; i++) {
          nums.push(i)
        }
        return nums
      } else {
        const num = Number(t)
        if (!num) {
          throw new RangeError(`bad track number: ${t}`)
        }
        return [Number(t)]
      }
    }).flat().map(t => `${curDisc}.${t}`)
    if (!parsed[curRole]) {
      parsed[curRole] = {}
    }
    for (const artist of artists) {
      if (!parsed[curRole][artist]) {
        parsed[curRole][artist] = new Set()
      }

      for (const track of tracks) {
        parsed[curRole][artist].add(track)
      }
    }
    continue
  }

  throw new RangeError(`could not parse line: ${line}`)
}

for (const [role, artistsAndTracks] of Object.entries(parsed)) {
  console.log(`${role}:`)
  for (const [artist, tracks] of Object.entries(artistsAndTracks)) {
    console.log(`${artist} (${[...tracks].join(', ')})`)
  }
  console.log('')
}